(1) Field of the Invention
This invention relates to a new and improved process for preparing sulfonated lignins and more particularly to a process for preparing sulfonated lignins of low viscosity possessing improved heat stability properties.
(2) The Prior Art
Dyestuff compositions generally comprise a dye cake, i.e., of disperse dyes or vat dyes, and a dispersant. These dyestuff compositions are widely used to color both natural and synthetic fibers. In the dyestuff composition, the dispersant serves three basic functions: (1) it assists in reducing the dye particle to a fine size; (2) it maintains a dispersing medium; and (3) it is used as a diluent.
Dye dispersants are generally one of two major types, sulfonated lignins from the wood pulping industry via the sulfite or kraft processes or napthalene sulfonates from the petroleum industry.
The advantages of employing sulfonated lignins as dispersants in dyestuff compositions is based on their unique physical properties which include good compatibility to many dye systems, outstanding dispersant characteristics at ambient and elevated temperatures and availability. There are, however, a number of disadvantages in employing lignins, whether they are sulfite lignins or sulfonated kraft lignins, as dispersants. These negative factors relate to fiber staining, heat stability and viscosity of the lignins employed. These adverse properties are troublesome to dyers and many attempts have been made to overcome these disadvantages.
A number of technological developments have resulted in new methods and processes to modify sulfonated lignins to reduce the negative aspects of employing such materials as dye dispersants without simultaneously causing any major adverse effects upon those properties which render sulfonated lignins desirable as dyestuff dispersants. U.S. Pat. No. 4,001,202, which names as a co-inventor the sole inventor in this application, describes a process for preparing a sulfonated lignin with improved fiber staining properties useful as a dye dispersant, by reacting such lignin with an epihalohydrin. Also, U.S. Pat. No. 4,338,091, issued to the inventor in this application, teaches reacting a modified lignin with sodium sulfite and an aldehyde. The lignin is modified, however, by a pretreatment with sodium dithionate; thus, the subsequent reaction does not involve the lignin material of the present invention.
Additional examples of reacting or modifying lignins to make them more suitable as dye dispersants include U.S. Pat. Nos. 4,184,845, 4,131,564, 3,156,520, 3,094,515, 3,726,850, 2,680,113, and 3,769,272. The art cited is meant to show the state of the art and is not intended to be all inclusive of lignin modifications.
Although the methods for treating and preparing sulfonated lignins described above offer some advantage during dyeing, none have produced a product possessing the improvements obtained by the products made according to the claimed process.
It is the general object of this invention to provide a process whereby sulfonated lignins or lignosulfonates may be prepared to improve their usefulness as dye dispersants.
Another object of this invention is to provide a process for reducing the viscosity of sulfonated lignins or lignosulfonates.
Another object of this invention is to provide a process for improving the heat stability of sulfonated lignins or lignosulfonates.
Other objects, features and advantages of this invention will be seen in the following detailed description of the invention.